Organosilicate coatings are usually prepared as two component systems which are mixed together shortly prior to use. The organosilicate portion of the coating is constituted by a resinous material carrying a plurality of silicon-carried alkoxy groups, this resinous material being itself a liquid or being dispersed or dissolved in a solvent or other volatile liquid. The second portion is a curing agent containing an amine or latent amine. When the two components are mixed together, the pot life is very short, normally less than about 20 minutes, so the systems must not only be prepared with care, but their use is difficult because the viscosity changes rapidly with time, and after a few minutes it is too late to use the mixture effectively.
The problem of shortened pot life due to the admixture of the resinous component containing silicon-carried alkoxy groups and amine curing agent is said to be solved to some extent for the production of silicone rubber films from organic solvent systems by the teachings of Canadian Pat. No. 680,886 to Votaw. Votaw teaches that a solvent solution of a mixture of a liquid to gummy diorganopolysiloxane and a liquid polyfunctional silane or siloxane can be applied as a film to a substrate and cured by exposing the film to the vapors of an amine or ammonia to form a silicone rubber film. There are, however, several drawbacks to Votaw's systems.
First, Votaw's compositions contain two silicon-containing components; a hydroxy-endblocked diorganopolysiloxane and a liquid cross-linking agent containing an alkyl trialkoxysilane, an alkyl orthosilicate or liquid partial hydrolyzates of either or both types of cross-linking agent. Thus, two different materials must be compounded to prepare the silicone rubber film. Additionally, diorganopolysiloxanes are relatively expensive and do not offer a wide range of film properties once they are cured, Votaw teaching only the preparation of silicone rubber films.
Second, the coating systems disclosed by Votaw are dissolved in an organic solvent such as xylene, toluene, benzene, hexane, butanol or 2-ethylhexanol. This fact leads to two other problems. The first is the skyrocketing cost of organic solvents which has occurred in recent years. The second problem with the use of organic solvents relates to the environmental and inflammatory effects of such solvents. For example, there is a potential health hazard to the workers who must breathe the vapors of Votaw's organic solvents when using his system. In addition, it is well known that solvents such as benzene, xylene, toluene and hexane are extremely flammable and the use of these solvents requires special explosion-proof apparatus.
On the other hand, the invention described hereinafter utilizes only one ingredient which contains a silicon atom, rather than the two silicon atom-bearing entities of Votaw, and because the compositions utilized in the instant invention are aqueous latex emulsions containing substantially no organic solvent, the environmental and flammability risks inherent in Votaw's systems are substantially eliminated.